New sealant compositions based on mercaptan-terminated polythioether polymer are provided. These compositions contain a unique combination of ingredients which was developed to utilize the inherent qualities of the polythioether polymer. The concept of using a polythioether polymer as the base polymer of a sealant has been published. For example, in U.S. Pat. No. 3,717,618 a mixture composed of a polythioetherdithiol, a plasticizer, a stearic acid, carbon black and lead dioxide becomes cured after storage in a controlled environment. The properties of the curred composition were not described. This patent indicated the polymerizability of a mercaptan terminated polythioether in the presence of compounding ingredients. However, considerable additional information is needed to prepare a practical, commercially-useful sealant having adequate work life and suitable curing time, hardness and good adhesive properties.
The properties of a sealant are dependent not only on the inherent contribution of the base polymer but also on the overall effect of the combination of ingredients making up the formulated sealant. As a result of my unique formulations, polythioether polymers can now be readily utilized as the reactive polymeric component of sealants which will meet the critical demands of sealant users. My novel formulations provide the means whereby polythioetherthiols can now be components of sealants meeting the real-life requirements of economics, and performance. These formulations both in the cured and uncured state are new compositions which are the vehicles whereby the superior inherent properties of the polythioetherthiols can be realized and utilized!
Elastomeric sealants find use in filling, binding and sealing joints and seams in many areas of construction including buildings and building components such as insulated glass windows, marine, aircraft and pavements.
These sealants are generally mixtures of a base polymer, a curing agent and several compounding ingredients. The compounding ingredients serve many purposes. They lower cost, provide thixotrophic properties and plasticization, improve adhesion, affect color, accelerate or retard cure and improve weatherability. A host of curing agents are employed.
Sealants derived from mercaptan-terminated base polymers are usually cured by oxidative coupling, although other systems utilizing epoxy compounds or isocyanates or other types of reagents are also useful. Organic or inorganic peroxides are generally employed to effect oxidative coupling of mercaptan-terminated polymer. Agents such as oxygen or sulfur are also effective. Manganese peroxide, calcium peroxide and lead peroxide are inorganic peroxides commonly used as oxidative curing agents. The technique in which they are compounded into the sealant formulation and other factors such as pH, particle size of the peroxide, the presence or absence of accelerating or retarding chemicals, relative humidity, and temperature affect the rate and extent of cure, and hence the useful properties of the sealant in the field.
The compounding ingredients are often interactive with each other, with the curing agents and with the base polymer. Sealant characteristics are often unpredictably affected by these interactions. Thus, for example, a plasticizer may lessen the highly desirable level of adhesion of the sealant to a concrete substrate or an adhesion additive may reduce the storage stability of the packaged sealant. The introduction of a new compounding ingredient or curing agent into a sealant formulation generally entails the adjustment of the other parameters of the system in order to retain the already realized valuable properties of the sealant as well to gain improved properties.
A major component of sealants is the base polymer. Its fundamental structure and hence its reactivity. stability, viscosity and other properties are of utmost importance in ultimately defining the performance of the sealant. Its properties with respect to its interaction with the curing agent and compounding ingredients are of major importance. One would expect, therefore, to see differences, when the mercaptan-terminated base polymer is replaced with a different mercaptan-terminated base polymer. These differences, seen as sealant physical properties, and curing and handling characteristics, would be due to the contribution of fundamental properties of the new polymer and also due to the interaction of the new polymer, in terms of compatability, reactivty, and other factors, with the compounding ingredients.
The differences in properties between sealants derived from different base polymers are not entirely obvious and are often unexpected. Employing a new base polymer will probably require the selection of new compounding ingredients in order to realize the full contribution of the new polymer to sealant properties. A new degree of uncertainty is introduced. The interaction of compounding ingredients is overlaid on the new set of characteristics of the new base polymer. Therefore, considerable insight is necessary to develop a sealant suitable for use in the field based on a new base polymer.
Many sealant formulations based on mercaptan-terminated polymers utilize the polysulfide liquid polymers of the type sold under the trade name "Thiokol". A body of knowledge concerning the application of standard or well-known compounding ingredients in sealant formulations has been built up during the last 20-30 years and much or most of this work has been directed toward formulations containing Thiokol polysulfide polymers.
Several prior art patents illustrate the state of the art, but as discussed below, the teachings of these references are distinguished from the present invention.
Oswald et al, U.S. Pat. No. 3,625,925 discloses a process for the preparation of polythioether products and suggests the use of such products in adhesive compositions, in admixture with various fillers, such as carbon black, oxidizers such as lead dioxide, calcium perioxide, and zinc peroxide, plasticizer such as dibutylphthalate and stearic acid as a cure retarder. The essential detail necessary to provide a useful sealant is not provided. Useful formulations based on necessary cure accelerators and adhesion additives and the interaction of specific constituents are neither disclosed nor suggested.
Oswald, U.S. Pat. No. 3,592,798 discloses a process for the preparation of certain low mol. wt. polythioether addition products and suggests the reaction of such products with reactants such as diisocyanates, epoxides, and others to form mastic compositions. Sealant systems based on oxidative curing agents such as MnO.sub.2 or PbO.sub.2 as in the present invention are not disclosed.
Stephenson et al, U.S. Pat. No. 3,629,206 discloses curing systems based on lead salts and alkylthiuram polysulfides, e.g., tetramethylthiuram disulfide, for use with organic polysulfide (i.e. "Thiokol" type) polymers. Neither the sealant systems nor the polythioethers of the present invention are suggested.
Millen, U.S. Pat. No. 3,637,574 discloses sealant compositions based on polysulfide polymers (not the polythioethers of the present application) cured with the aid of a zinc compound and a tetraalkylthiuram disulfide. The base polymer as well as the other critical sealant constituents differ substantially from those of the present sealant system.
Guthrie, U.S. Pat. No. 3,640,923 discloses curable adhesive compositions formed by adding an oxime such as quinone dioxime to a liquid composition comprising a polyene and a polythiol in the presence of an iron or iron compound to accelerate the cure. The dioxime is added to a system wherein not only the base polymer but the various other constituents of the system differ considerably from those of the present sealant system.
Bulbenko, U.S. Pat. No. 3,328,451 discloses the use of mercaptoalkyl amino alkylalkoxy silane compounds as adhesive additives in polysulfide polymer based systems. Sealant systems based on the polythioethers employed in the present compositions are not disclosed.
Oswald et al, U.S. Pat. No. 3,859,360 relates to thioether mastic and pesticide compositions prepared from the products of free radical addition of monothiols or dithiols to diallylic sulfides. The reference compositions are distinguished from those of the present invention in being devoid of recurring propylene groups as integral units of a thioether polymer chain and any trivalent substituted cyclohexane groups.